Oil burner apparatus



May 1967 E. c. BRIGGS ETAL 3,316,955

OIL BURNER APPARATUS Filed March 8, 1965 2 Sheets-Sheet 1 INVENTORS [066! c. ate/as s 19/96 F F/Yff/VS' i m d W P 23% ATTORNEYS OIL BURNER APPARATUS Filed March 8, 1965 Fig-Q 2 Sheets-Sheet 2 M P 3M ATTORNEYS United States Patent 3,316,955 OIL BURNER APPARATUS Eugene C. Briggs, Dayton, and Ralph Farkas, Wilmington, Ohio, assignors to Master Consolidated Inc., Dayton, Ohio, a corporation of Ohio Filed Mar. 8, 1965, Ser. No. 437,888 13 Claims. (Cl. 158-4) This invention relates to apparatus providing an improved combustion chamber for oil burners and like equipment.

A primary object of the invention is to provide a combustion chamber for oil burners and like equipment which is economical to fabricate, more efficient and satisfactory in use, adaptable to a wide variety of applications and unlikely to cause malfunction.

Another object of the invention is to provide a burner unit with an improved combustion chamber enabling a cleaner and more effective burning of the applied fuel.

A further object of the invention is to provide a novelly fabricated combustion chamber.

Another object of the invention is to provide oil burners and like equipment with a combustion head the use of which minimizes the deposit of carbon on burning the applied fuel.

An additional object of the invention is to provide oil and like burner units with a combustion chamber wherein fuel is so vaporized to enable optimal combustion.

Another object of the invention is to provide an improved combustion chamber for oil burners and like equipment the operation of which produces an afterburning effect enabling a more efficient and complete use of the applied fuel.

A further object of the invention is to provide a combustion chamber for oil burners and like equipment pos sessing the advantageous structural features, the inherent meritorious characteristics and the means and mode of use here described.

With the above and other incidental objects in view as will more fully appear in the specification, the invention intended to be protected by Letters Patent consists of the features of construction, the parts and combinations thereof, and the mode of operation as hereinafter described or illustrated in the accompanying drawings or their equivalents.

Referring to the accompanying drawing wherein is shown one but obviously not necessarily the only form of embodiment of the invention,

FIG. 1 is an elevation view of an oil burner in combination with means defining an improved combustion chamber in accordance with the present invention;

FIG. 2 is a cross-sectional view of the orifice cup and vaporizer tube portions of the combustion chamber;

FIG. 3 is an end view of the structure shown in FIG. 2;

FIG. 4 is a view, in longitudinal section, of the housing for the structure of FIG. 2, which housing embodies a turbulator;

FIG. 5 is a view of the entrance end of the structure shown in FIG. 4;

FIG. 6 is a plan view of the turbulator per se; and

FIG. 7 is a fragmentary cross-sectional view of the turbulator.

Like parts are indicated by similar characters of reference throughout the several views.

Seen in FIG. 1 of the drawings is a shell-like housing 10 having at one end thereof a perforated air inlet panel 11 and at its opposite end a mounting panel 12. The panel 12 has a large generally central opening 13.

An oil burner 14 is contained in the housing 10. The burner as illustrated includes a motor, a fan, a compressor and a burner head, all of which are integrally connected in generally aligned relation.

The burner is fixedly supported in the housing 10 by means of a clamp type bracket 15 which engages about its motor 16. Fixed to one end of the motor 16, relatively adjacent the panel 11, is a shell-like sheet metal structure forming a chamber 17 for a sirocco type fan 18. The fan 18 mounts on one end of the motor drive shaft 19 which positions interiorly and centrally of the shell forming the chamber 17. The wall of the chamber 17 most adjacent the panel 11 has a substantial central open ing the edge of which flares inwardly of the chamber to cup about and in spaced relation to the radially innermost portions of the fan blades 20. This wall is radially extended to otherwise form a transverse seal of the housing 10. The peripheral wall of the chamber 17 is provided with a series of circumferentially spaced slots 21.

Fixed to form a direct axial extension of the motor 16 to its end remote from the shell 17 is an air compressor 22 which in turn fixedly supports a burner head 23. The head 23 includes an atomizing nozzle 24 exposed centrally of a recess formed by a shell-like extension 25. The head portion 25 projects through the center of the opening 13 in the end panel 12 of the housing 10.

For purpose of illustrating the present invention, the details of the oil burner need not be described except in a general way since such details are not essential to an understanding of the invention. However, for purposes of this disclosure, it is to be understood that the compressor 22 is of a type that its rotor mounts to and turns with a projected end portion of the motor drive shaft 19. Moreover, the compressor is provided with an air inlet opening through a filter to the interior of the housing 10 and a discharge passage which communicates with a flow passage in the burner head which eventually leads to an air intake passage in the atomizing nozzle 24. The burner head also conventionally includes a flow passage connected at one end to a supply of fuel and at its other end to the air flow passage in the atomizintg nozzle 24.

It is to be noted that a burner unit of the type described is generally provided with slots at its head portion 25 to enable a tangential inflow of air to and about the atomizing nozzle 24. This insures an effective delivery of the atomized fuel which issues from the nozzle.

As shown in FIG. 1 of the drawings, the housing 10 has its end panel 12 fixed to a support plate 26. The plate 26 has an opening larger than the opening 13 and in coaxial relation thereto. In this manner a portion of the end panel 12 immediately about the opening 13 is exposed. In the practice of the invention as illustrated this panel portion serves to seat the peripheral flange 27 on the open end of a projected orifice cup 28. The flange 27 is suitably secured to the panel 12.

The cup 28 has a central portion of its base 29 offset outwardly of the housing 10 to nest the projected extremity of the head portion 25. The cup 28 thereby forms a shield which bridges the opening 13 in the panel 12. As formed, the peripheral wall portion of the cup positions about and in spaced relation to the burner head portion 25. The cup base has a limited aperture 30 which exposes the discharge end of the nozzle 24. Noting the drawings, it may be seen that the burner head mounts an i-gniter 24' the operative tip of which positions at the aperture 30, immediately over and adjacent the discharge end of the nozzle. An imperforate tube 31 has one end thereof secured about the peripheral wall of the cup 28. So positioned, the tube 31 forms a housing which projects perpendicular to the panel 12. Mounting within and in concentrically spaced relation to the tubular housing 31 is a second imperforate and relatively shorter tube 32. One end of the tube 32 is press fit to peripherally encompass the relatively projected base portion of the cup 28 which in turn nests the projected extremity of the burner head portion 25. Circularlyspaced portions of the cup mount- 3 :d end of the tube 32 are relatively offset to abut the inier wall of the tube 31. In this manner an appropriate :pacing is maintained between the housing shell 31 and ;he relatively adjacent inner tube 32.

Referring to FIG. 3 of the drawings, it may be seen that the portion of the cup 28 which positions intermediately of the tube 31 and 32 includes circumferentially spaced slots 33 opening to the one side to the space in the housing about the burner head 23 and to the other side to the space between the tubes 31 and 32.

Positioned within and in concentrically spaced relation to the tube 32 is a vaporizing tube 34. The tube 34 positions coaxial with the cup aperture 30 and has its entrance end substantially spaced from the base of the orifice cup 28. Formed integral with the entrance end of the tube 34 are circularly spaced axially projected mounting tabs 35. The projected extremities of the tabs 35 are inserted through slots in the cup base 29 and bent to secure the tube to the cup in a manner believed obvious.

Viewing FIG. 1 of the drawings, it may be seen that not only is the entrance end of the vaporizing tube 34 spaced from the cup 28 but its discharge extremity is projected relative the tube 32 to terminate in a plane just short of that defined by the projected extremity of the housing tube 31. The latter mounts a cap-like element 36 having a cuplike contour opening to the interior of the housing the base of which has a substantial central aperture 37. The diameter of the aperture 37 is greater than the diameter of the adjacent end of the vaporizing tube 34. An annular turbulator plate 38 has the periphery thereof anchored by tabs to the interior surface of the tube 31. The turbulator plate extends transverse to the tube 31 in concentric spaced relation to the discharge end of the vaporizer tube 34, in a plane immediately adjacent and spaced beyond the pro- -jected extremity of the intermediate tube 32.

Viewing FIGS. 6 and 7 of the drawings, it may be seen that the turbulator plate has a series of circularly spaced portions 39 which are relatively offset in opposite senses to have portions project from the opposite faces of the plate. The angular positions of the relatively offset portions 39 are such to dispose them in a circularly following sense. Accordingly, each of the portions 39 is inclined to the plane of the plate 38. Each portion includes a relatively central aperture 40 the central axis of which is similarly inclined.

The apparatus as above described provides a combustion chamber in accordance with the invention which in total includes the tubular housing 31, the orifice cup 28 which forms a shield to its entrance end and exposes the fuel injector device exemplified by the atomizing nozzle 24, the intermediate tube 32, the vaporizing tube 34, the turbulator plate 38 and the cap element 36.

It may be seen that the base 29 of the orifice cup overlies the discharge face of the burner head 23 except for the central limited aperture 30 exposing the nozzle 24 and igniter 24'. By this means, as will become obvious the cup affords a heat and radiation shield for the burner components as well as a control shield for the air to be heated in passage through the combustion chamber.

In use of the above described apparatus, energizing the motor 16 produces a drive of its shaft 19 and a simul taneous drive of the fan 18 and the rotor of the compressor 22. The fan 18 operates to draw air through the openings in the panel 11 to the interior of the chamber 17 and expel it in a positively pressured flow through the peripherally spaced slots 21. This fan driven air moves inwardly of the housing 10 over the motor and past the compressor 22. The simultaneously operating compressor draws a portion of this air interiorly thereof under the influence of its spinning rotor. The rotor discharges the air under increased pressure to flow to and through the communicating air passage in the burner head 23 and eventually escape through the air passage in the atomizing nozzle 24. This pressured flow of air through the nozzle 24 results in an aspiration of fuel from the connected source of supply, in the process of which the fuel is mixed with and atomized by the air as it exists from the nozzle.

The major portion of the air which flows from the fan 18 passes the compressor to move about the burner head portion 25 through the cup slots 33 and exit in an accelerated flow to the space between the housing tube 31 and the inner tube 32 of the apparatus defining the combustion chamber. A portion of the air which enters the orifice cup on passage to the slots 33 is diverted through the slots in the burner head portion 25 to move inwardly and about the nozzle 24 to assist the discharge therefrom of the atomized fuel and its projection interiorly of the vaporizing tube 34.

The fuel is ignited on discharge but there is a nonluminous burning until it reaches a point well within the vaporizing tube.

In the described system, the fuel air mixture entering the vaporizing tube 34 is such that it is starved for air. As luminous burning first occurs interiorly of the tube 34, it creates a low pressure area and produces an aspiration thereto of additional air entering the combustion chamber. The major portion of this air is drawn in to the vaporizing tube through the space between its entrance end and the base of the orifice cup 28. A portion of the air drawn in comes directly from the slots 33 in the orifice cup and through the openings in the inner tube 32 provided by its offset portions fixed in abutment with the inner wall of the housing tube 31.

In the main the inner tube 32 serves as a recirculation tube. The major portion of the pressured air which flows through the slots 33 moves over the outer surface of the tube 32 until it reaches the turbulator plate 38 at which point a portion thereof is induced by impingement on the turbulator plate and the influence of the low pressure area in the vaporizing tube to flow inwardly between the vaporizing tube 34 and the inner wall of the tube 32 and enter the tube 34 through its entrance end. This is enabled by the spacing of the vaporizing tube from the cup 28. The effect of this additional air flow about the recirculating tube 32 is to insure that the additional air reaching the tube 34 in this manner is well preheated. The result of this is optimal vaporization of the fuel within the vaporizing tube and better burning.

The portion of the pressured flow of air which moves through the apertures 40 in the turbulator plate 38 is caused thereby to swirl in and about the projected extremity of the vaporizing tube. The effect of this swirling air is to cause unburned particles of fuel which issue from the vaporizing tube in the body of the projected flame produced by burning of the fuel in the tube to move inwardly of the flame and be consumed in the process. Thus, within the combustion chamber there is produced a pressured flow of air which is recirculated after passage through the orifice cup and heated and reheated in process of movement through the combustion chamber. Such air feeds the ignited fuel. The result is an optimal fuel vaporization and combustion and a maximum efiiciency in converting the available heat content of the utilized materials to a useful purpose.

It is contemplated in a preferred embodiment of the invention that the diameter of the vaporizing tube be such in reference to the angle of spray which issues from the associated fuel injector nozzle that the spray particles do not directly impinge on the inner surface of the tube. By this means the invention prevents cooling of the ignited fuel to any degree that it will not burn satisfactorily. Moreover, this feature avoids a possibility of burning occurring on the outside of the vaporizing tube and thereby avoids the formation of carbon deposits which may eventually create annoying maintenance problems in operation of the burner units.

Accordingly, the improved combustion chamber as provided by the present invention enables an optimal output from any burner unit to which is it applied. Moreover, the displacement of the vaporizing tube from the nozzle of the burner unit results in better spark plug action and a cooler nozzle. The added air circulation within the combustion chamber per se is at a high velocity due to the arrangement of its components. A better breakdown of the fuel mixture occurs in the vaporizing tube and the recirculating of preheated air to enter the entrance end of the vaporizing tube enhances the capacity of the combustion chamber to produce optimal results.

From the above description it will be apparent that there is thus provided a device of the character described possessing the particular features of advantage before enumerated as desirable, but which obviously is susceptible of modification in its form, proportions, detail construction and arrangement of parts without departing from the principle involved or sacrificing any of its advantages.

While in order to comply with the statute the invention has been described in language more or less specific as to structural features, it is to be understood that the invention is not limited to the specific features shown, but that the means and construction herein disclosed comprise but one of several modes of putting the invention into effect, and the invention is therefore claimed in any of its forms or modifications within the legitimate and valid scope of the appended claims.

Having thus described our invention, we claim:

1. Apparatus providing a combustion chamber for oil burners and like equipment including a shell providing a housing open to opposite ends, a shield fixed transversely of one end having limited openings respectively providing for receipt in and movement through said shell of a pressured flow of air and receipt of charges of fuel which are ignited in the process of their delivery in said shell, a vaporizing tube fixed centrally of said shell having one end opposite and spaced from said shield, arranged thereby to receive the charges of fuel, and its other end adjacent and open to the other end of said shell, a tubular element defining with said shell a flow path for air entering said shell under pressure and forming with said shell and about said vaporizing tube a path for recirculating a portion of such air under the influence of combustion in said tube whereby to provide preheated air in said tube producing an optimal vaporizing of the fuel which enters said tube and means adjacent said other end of said vaporizing tube operative to produce a circulation of the air flowing to said other end of said shell in a sense to cause said air to pick up unburned particles leaving said vaporizing tube and drive them inwardly of the flame produced by combustion in said tube.

2. In combination a burner unit including an exposed fuel injector, igniter, and means for producing a pressured flow of air, a housing consisting of a shell of generally tubular form having at one end thereof a cap for said burner unit including limited openings exposing the delivery end of said fuel injector and igniter and providing for at least a portion of said pressured flow of air to enter and pass through said shell, a vaporizing tube within said shell one end of which is aligned with and spaced longitudinally from said cap and fuel injector, said injector and igniter being operatively related to deliver a charge of fuel to said tube burning in a non-luminous condition, means in said housing to provide a directed flow of a portion of said air to enter said one end of said tube whereby luminous burning occurs interiorly of said tube and means in said housing operative on air which moves thereby to produce a circulation of such air in a manner to drive unburned fuel particles inwardly of the flame produced by combustion in said tube.

3. The combintaion as set forth in claim 2 characterized by said fuel injector discharging fuel in a predetermined spray form and said vaporizing tube having a position and dimension relative said spray form to substantially avoid impingement of the sprayed fuel particles on its inner wall.

4. Apparatus providing a combustion chamber for oil burners and like equipment which includes a burner head having an exposed fuel injector, igniter means and, in combination therewith, means for producing a pressured flow of air about said head, comprising means defining a shield for said head having a limited aperture for exposing the discharge extremity of the fuel injector and the operating tip of said igniter, a first in l-perforate generally tubular element fixed to project from said shield having one end positioning about and in spaced relation to said aperture, a second relatively shorter tubular element fixed within and in spaced adjacent relation to said first element to form therebetween a flow passage, a third tubular element Within and spaced from said second element, said third element positioning in a generally axial alignment with said aperture, means defining at least one opening in said shield between said first and second elements for delivery of at least a portion of the air flowing about said burner head through said flow passage, at least one opening in said second tubular element adjacent said shield, said third element having one end thereof spaced from said shield and the other end thereof extending to a plane adjacent and spaced from the other end of said first tubular element, said third element operating to define a combustion area receiving ignited fuel and producing a burning thereof in a manner to induce an inflow of air and an inherent vaporizing of the delivered fuel, the process being facilitated by the spacing of said third element from said shield.

5. Apparatus providing a combustion chamber for oil burners and like equipment comprising an imperforate shell-like housing open to opposite ends, means forming a shield closing one end of said housing, said shield being adapted to cap a burner unit and having a limited opening for exposing the discharge extremity of its fuel injector, a vaporizing tube fixed in said housing to have an axial spaced alignment referenced to the opening in said shield and consequently said fuel injector, means provided for passage through said shield of a pressured flow of air, said vaporizing tube defining a combustion area arranged to receive the fuel injected in said housing, burning of the fuel in said housing producing a low pressure area and an aspiration to said vaporizing tube of additional air the entrance of which is facilitated by the spacing of the vaporizing tube from said shield.

6. The structure as set forth in claim 5 characterized by a turbulating plate fixed about and in spaced relation to said tube in transverse relation to said housing including circularly spaced portions offset in a circularly following sense and apertured to pass air therethrough in a whirling fashion, which air function to pick up unburned particles of fuel which issue from the vaporizing tube and drive them inwardly of the flame produced by combustion in said vaporizing tube.

7. Apparatus providing a combustion chamber for oil burners and like equipment comprising an orifice cup for capping a burner head to form an air pocket thereabout and provide an opening for discharge of fuel from said head, said cup having passages opening to the air pocket, means defining a housing one end of which is bridged by said cup and the opposite end which is open, a vaporizing tube concentrically positioned within said housing to have its entrance end which receives the fuel spaced from said cup, aligned therewith, and its exit end adjacent the open end of said housing, means in said housing defining a path for the flow of air from said passages in an area spaced outwardly from the vaporizing tube to be heated in passage during burning of fuel in said vaporizing tube and forming with said vaporizing tube a recirculating path for the heated air to provide that on combustion of fuel in said vaporizing tube preheated air may be induced to enter its entrance end and thereby produce therein an optimal vaporizing of the fuel, said means defining said recirculating path including .a tube, one end of which engages said cup, said last-mentioned tube extending in concentric spaced relation to said vaporizing tube nd terminating short of its exit end, and a turbulator late positioned transversely of said housing about the xit end of said vaporizing tube and in end spaced relaon to the projected extremity of said means defining aid recirculating path aforementioned, said turbulator late including circularly spaced portions offset in a cirular sense having apertures for inducing the air which asses through said plate to swirl around the said open rid of said housing, pick up unburned fuel particles which ssue from said vaporizing tube and drive them inwardly )f the flame produced by combustion in said tube.

8. Apparatus providing a combustion chamber for oil urners and like equipment which includes a burner head raving an exposed fuel injector and, in combination therevith, igniter means and means for channelling a pressured low of air about said head, comprising means forming a :hield for said head having a limited aperture to provide :xposure of the discharge end of said fuel injector, imierforate tubular means connected to project from said ;hield in end spaced relation to the discharge end of said fuel injector, a pair of tubes, the walls of which are radially spaced, mounting to project generally perpendicular to said shield and about said tubular means, the inner of said tubes being shorter and the outer longer than said tubular means, said shield means being apertured between said tubes and said tubular means being formed to provide a path for a circulating pressured flow of air to enter the end of said tubular means adjacent and spaced from said shield.

9. Apparatus as set forth in claim 8 characterized by a turbulator plate fixed transverse to the outer of said tubes and extending radially inward thereof to overlap the inner of said tubes in end spaced relation thereto, said turbulator plate being apertured to produce a circular flow of air about the outer end of said tubular means.

10. In an oil burner or the like wherein housing means having air under pressure flowing therethrough has an outlet at one end for discharge of the flowing air, a nozzle being disposed in said housing for discharge of a fuel mixture through said outlet, an improved combustion head comprising capping means installed in an overlying relation to the burner head, exposing the discharge end of said nozzle, said cap having a central opening spaced from said nozzle and through which the nozzle discharges, the spacing of said nozzle and cap being such that a part of the air flowing to the housing outlet may escape through said central opening in an intimate mixing relation to the fuel mixture discharging from the nozzle, said cap having other outwardly located openings through which another part of the air flow may escape, a vaporizing tube disposed longitudinally beyond said cap means, in axially spaced relation to the central opening therein and to the nozzle, said tube having entrance and exit ends, the entrance end substantially exceeding in diameter the diameter of the central opening in said cap, the spacing of said tube and the diameter thereof being such that the projected discharge from the nozzle bridges the space between the nozzle and tube and is received in the tube substantially without impingement on the interior of the tube wall, a portion of said second part of the air flow entering the entrance end of said tube and another portion passing over the exterior of the tube wall and in through the exit end thereof, and an air confining housing extension in surrounding spaced relation to said tube.

11. An improved combustion head according to claim 10 characterized by a turbulator plate installed in surrounding spaced relation to said tube adjacent its exit end, said plate having flow passages therein which are per se angled and further defining with said tube an annular flow path therebetween, the said other portion of said air flow dividing into a first stream flowing through said annular path and into the exit end of said tube as described and a second stream forced through said angled flow passages, the angle of said passages being such to utilize the air flow therethrough to inhibit the radial escape of unburned fuel particles from flame issuing from the exit end of said tube during combustion.

12. An improved combustion head according to claim characterized by a tubular element intermediate said tube in said housing and laterally spaced relative to both thereof, one end of said tubular element being interengaged with said cap at a location between said central opening in said cap and said other outwardly located openings, said tubular element having outstruck portions engaging said housing to position said tubular element and to define openings interconnecting the spaces on opposite sides of said element, the said other portion of said second part of said air flow being subdivided into flows on opposite sides of said tubular element, said tubular element terminating at its opposite end short of the exit end of said tube.

13. In an oil burner or the like wherein housing means having air under pressure flowing therethrough has an outlet at one end for discharge of the flowing air, a nozzle being disposed in said housing for discharge of a fuel mixture through said outlet, an improved combustion head comprising cap means installed in a covering relation to the burner head to expose the discharge opening of said nozzle, a spacing being provided between said nozzle and cap such that a part of the air flowing to the cap may escape through a central opening therein providing the aforementioned exposure and be thereby intimately mixed with the fuel mixture discharging from said nozzle, said cap having other outwardly located openings through which another part of the air flow may escape, and a tubular assembly projected forwardly of said cap comprising in concentric relation a housing and a nested tube, said cap having offset projected portions respectively achieving a telescoping relation to said housing and said nesting tube, the said other openings in said cap communicating with the space between said housing and said tube, said tube having outstruck portions engaging said housing arranged to position said tube and to communicate the space with the interior of said tube, said tubular assembly further comprising a vaporizing tube surrounded by said nesting tube and aligned with the central opening in said cap, the end of said vaporizing tube adjacent to said cap means receiving the discharge from said nozzle and constituting the entrance end of the vaporizing tube, said entrance end being longitudinally spaced from said nozzle by formations thereon which project into interengaging relation with said cap, the said other part of the air flow dividing into a portion entering the entrance end of said vaporizing tube and other portions flowing longitudinally on opposite sides of said intermediate tube to the opposite or exit end of said vaporizing tube.

References Cited by the Examiner FOREIGN PATENTS 870,988 6/1961 Great Britain.

FREDERICK L. MATTESON, JR., Primary Examiner.

DONLEY I. STOCKING, Examiner.

E. G. FAVORS, Assistant Examiner. 

1. APPARATUS PROVIDING A COMBUSTION CHAMBER FOR OIL BURNERS AND LIKE EQUIPMENT INCLUDING A SHELL PROVIDING A HOUSING OPEN TO OPPOSITE ENDS, A SHIELD FIXED TRANSVERSELY OF ONE END HAVING LIMITED OPENINGS RESPECTIVELY PROVIDING FOR RECEIPT IN AND MOVEMENT THROUGH SAID SHELL OF A PRESSURED FLOW OF AIR AND RECEIPT OF CHARGES OF FUEL WHICH ARE IGNITED IN THE PROCESS OF THEIR DELIVERY IN SAID SHELL, A VAPORIZING TUBE FIXED CENTRALLY OF SAID SHELL HAVING ONE END OPPOSITE AND SPACED FROM SAID SHIELD, ARRANGED THEREBY TO RECEIVE THE CHARGES OF FUEL, AND ITS OTHER END ADJACENT AND OPEN TO THE OTHER END OF SAID SHELL, A TUBULAR ELEMENT DEFINING WITH SAID SHELL A FLOW PATH FOR AIR ENTERING SAID SHELL UNDER PRESSURE AND FORMING WITH SAID SHELL AND ABOUT SAID VAPORIZING TUBE A PATH FOR RECIRCULATING A PORTION OF SUCH AIR UNDER THE INFLUENCE OF COMBUSTION IN SAID TUBE WHEREBY TO PROVIDE PREHEATED AIR IN SAID TUBE PRODUCING AN OPTIMAL VAPORIZING OF THE FUEL WHICH ENTERS SAID TUBE AND MEANS ADJACENT SAID OTHER END OF SAID VAPORIZING TUBE OPERATIVE TO PRODUCE A CIRCULATION OF THE AIR FLOWING TO SAID OTHER END OF SAID SHELL IN A SENSE TO CAUSE SAID AIR TO PICK UP UNBURNED PARTICLES LEAVING SAID VAPORIZING TUBE AND DRIVE THEM INWARDLY OF THE FLAME PRODUCED BY COMBUSTION IN SAID TUBE. 